The present invention relates to a semiconductor device and a method for Manufacturing the same, in which a semiconductor layer is formed using selective epitaxial growth on a semiconductor substrate, and more particularly to a semiconductor device and a method for manufacturing the same in which the shape of an oxide film used as a mask for performing selective epitaxial growth is optimized.
FIG. 1 shows a structure of an example of a semiconductor device formed by means of element isolation using selective epitaxial growth.
According to the conventional art, when an N-type silicon substrate 50 having the (100) plane is subjected to selective epitaxial growth using a silicon oxide film (SiO.sub.2) 52 as a mask at a high temperature (1000.degree. C.), a pattern edge of the silicon oxide film 52 as shown in FIG. 1 is formed. At this time, a P-type epitaxial layer 54 is grown upward along a silicon monocrystal (100). In other words, the P-type epitaxial layer 54 is grown in the same orientation as that of the silicon substrate 50. Further, a complex layer comprising an epitaxial layer 56 and a polysilicon layer 58, having different orientations, is formed in a boundary portion between the silicon oxide film 52 serving as a mask and the epitaxial layer 54.
It is assumed that the semiconductor device as shown in FIG. 1 constitutes a diode and that a reverse bias is applied to a junction between the N-type silicon substrate 50 and the epitaxial layer 54. In this case, since the complex layer comprising the epitaxial layer 56 and the polysilicon layer 58 is formed in the boundary portion between the silicon oxide film 52 and the epitaxial layer 54 as described above, a great junction leakage current is generated near the pattern edge of the silicon oxide film 52, i.e., in an end portion of the junction. This is because carriers are recombined in that part of the polysilicon layer 58 which is formed near the pattern edge of the silicon oxide film 52.